In-situ emulsification synergistic self-profile control system on heavy oil reservoir development: Prescription construction and EOR mechanism investigation

Abstract

Water flooding is a vital method used for developing heavy oil reservoirs. However, the fingering phenomenon is common because of the significant difference in water-oil mobility ratio, resulting in limited sweep efficiency and a low cumulative recovery factor. Viscosity reduction through emulsification and profile control using foam is of great potential to enhance oil recovery (EOR) in water flooding of general heavy oil reservoirs. The present work constructed an effective in-situ emulsification synergistic self-adjusting profile control system based on these two EOR pathways and investigated the performances of the proposed system, such as viscosity reduction via emulsification, foam plugging, and synergistic oil displacement. The results show that sodium octadecyl phenol polyoxyethylene ether sulfonate-4 (JNPM) with sound viscosity reduction, profile control, and oil displacement effects were synthesized through chlorination and sulfonation reactions. JNPM can reduce the oil-water interfacial tension and promote the emulsification of heavy oil in an effective way. It forms an unstable micron-scale oil-in-water emulsion, which is easy to induce oil-water separation of the produced fluid. The reduction in viscosity for JNPM exceeds 90%, whereas the foam produced by JNPM can adequately reduce the relative permeability of the displacement medium, and it is found that the resistance factor is higher than 25. The EOR mechanisms of JNPM include the following aspects. JNPM foam fluid has a stable plugging capability on the channeling channels of the displacement media, such as water and gas, which forcefully increases the residual oil sweep efficiency. JNPM peels off the residual oil on the pore wall through emulsification, thus the oil washing efficiency is improved. The droplets of oil formed by emulsification can block the channeling channels through the Jamin effect to further increase the conformance efficiency. In addition, when the small droplets deform and pass through the pores, they can sweep away the residual oil by dragging and entraining effects. The contributions of viscosity-reducing emulsification and foam plugging to EOR are 26.4% and 12.0% respectively during the viscosity-reducing foam flooding of JNPM.